1. Field
The disclosed concept pertains generally to secondary terminal blocks and, more particularly, the disclosed concept pertains to apparatus and methods for isolating the secondary terminal blocks and associated wiring in electrical switching assembly enclosures.
2. Background Information
Electrical switching assemblies are generally well known in the art and include, for example, circuit switching devices and circuit interrupters, such as circuit breakers, contactors, motor starters, motor controllers and other load controllers. Circuit breakers are used for protecting electrical circuitry from damage due to an over current condition, such as an overload condition or a relatively high level short circuit or fault condition. Molded case circuit breakers, for example, include at least one pair of separable contacts which are operated either manually by way of a handle disposed on the outside of the case or automatically by way of an internal trip unit in response to an over current condition. In the automatic mode of operation, an electronic trip unit, for example, controls an operating mechanism that opens the separable contacts. In the manual mode of operation, the handle cooperates with the operating mechanism in order to open the separable contacts. Circuit breakers have at least one line terminal for connection to a power source and at least one load terminal for connection to a load, such as a motor. The separable contacts of the circuit breakers are internally connected to the line and load terminals. Circuit breakers may also have one or more auxiliary terminals. Such auxiliary terminals may be utilized as inputs to provide an external signal for tripping the circuit breaker. Furthermore, other such auxiliary terminals may be utilized as outputs to externally indicate the trip status of the circuit breaker.
Typically, electrical switching assemblies, e.g., circuit breakers, are contained within enclosures. The enclosures are effective to protect the electrical switching assemblies from exposure to environmental conditions. The enclosures typically include at least one circuit breaker, internal components and a terminal block positioned therein. Terminal blocks are generally known electrical connector devices which are employed for joining two or more wires to a single connection point. Terminal blocks include a plurality on input connections and a plurality of output connections for receiving a plurality of control wires. Terminal blocks are used to electrically connect or interface components of an electrical system or electrical components within a mechanical system. Terminal blocks can be used to connect control wiring among various items of equipment within an enclosure or to make connections among individually enclosed items. The terminal blocks are structurally coupled to a surface of the enclosure by using a snap-in or screw-mounted mechanism. In conventional electrical switching apparatus, one or more first terminal blocks can be used to support first components and one or more secondary terminal blocks can be used to support secondary components in secondary control circuits.
Terminal blocks are generally not very well protected from contact with personnel or foreign conducting materials. In conventional circuit breaker enclosures, the secondary terminal blocks are not isolated from the breaker compartment. As a result, the secondary terminal blocks may not be capable to withstand the temperature and pressure effects of an electrical arcing fault which occurs in the breaker compartment.
Accordingly, there is room for improvement in known electrical switching assembly, such as circuit breaker, enclosures which contain secondary terminal blocks. It is desired that a compartment, e.g., isolation chamber, be designed and developed to enclose or house the secondary terminal blocks and associated wiring. This isolation chamber would be capable of isolating the secondary terminal block area from other components of the circuit breaker enclosure and, to withstand the temperature and pressure effects of an electrical arcing fault which may occur in the breaker compartment. It is further desired that the isolation chamber be adaptable to accommodate various switchgear and breaker configurations and sizes. Moreover, it is desired that the isolation chamber enhance the current arc resistant low voltage switchgear assembly by allowing personnel access to the secondary terminal blocks while maintaining the arc resistant rating.